Re: crashme fault

From: Randy Dunlap
Date: Mon Sep 17 2007 - 10:31:18 EST


Linus Torvalds wrote:

On Sun, 16 Sep 2007, Randy Dunlap wrote:
I'll test this overnight on 2.6.23-rc6-git2 since that was failing.

I haven't been able to reproduce the fault on 2.6.21 after several
hours of testing.

I'll also test a microcode update to see if it helps.

Before you do the microcode update, try to see if you can bisect the place between 2.6.21->22 that seems to start it. Even if you don't get all the way, if you are confident enough about the "no error" case to be able to bisect it down by doing a few reboots, it will at least cut down the set of possible commits by roughly a factor of 2^<nr-of-bisect> events, so even "just" a series of 4-5 bisect things might give us more of a clue.

OK, I haven't done the microcode update yet. I ran crashme overnight
with your newer patch and it crashed:

[14254.327676] Unable to handle kernel paging request at 00000000ff021eaf RIP: [14254.332299] [<0000000000504225>]
[14254.338084] PGD d8542067 PUD 0 [14254.341271] Oops: 0000 [1] SMP [14254.344449] CPU 3 [14254.346484] Modules linked in: loop
[14254.350001] Pid: 28565, comm: crashme Not tainted 2.6.23-rc6-git2 #2
[14254.356349] RIP: 0033:[<0000000000504225>] [<0000000000504225>]
[14254.362376] RSP: 002b:00007fff5afccbf8 EFLAGS: 00010656
[14254.367685] RAX: 000000005afccbf8 RBX: 00002abd4fbf5c00 RCX: 00002abd4fc88b37
[14254.374812] RDX: 0000000000504220 RSI: 0000000000000000 RDI: 000000000000000a
[14254.381939] RBP: 00007fff5afccc00 R08: 00007fff5afccb50 R09: 0000000000000000
[14254.389068] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
[14254.396195] R13: 00007fff5afccdf0 R14: 0000000000000000 R15: 0000000000000000
[14254.403324] FS: 00002abd4fe276d0(0000) GS:ffff81011fc751c0(0000) knlGS:0000000000000000
[14254.411403] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[14254.417144] CR2: 00000000ff021eaf CR3: 00000000d85f6000 CR4: 00000000000006e0
[14254.424273] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[14254.431400] DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
[14254.438528] Process crashme (pid: 28565, threadinfo ffff8100d8970000, task ffff8100d8628820)
[14254.446953] [14254.448443] RIP [<0000000000504225>]
[14254.452124] RSP <00007fff5afccbf8>
[14254.455614] CR2: 00000000ff021eaf
[14254.459244] Kernel panic - not syncing: Fatal exception


Of course, if it's somewhat random and timing-dependent, bisection can be hard (the "2^n" thing is very efficient, but it also means that a *single* wrong answer will totally invalidate the result, so if something isn't entirely reproducible, bisection often fails!)

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